The present invention relates to beverage dispensers for cooling a beverage to an acceptable temperature for consumption. In this regard, there are various distinct types of chilled beverage dispensers in the industry. Each, however, requires some sort of cooling system, typically a source of a cooling medium (such as a compressor and pump), a heat exchanger, and connecting tubing between the heat exchanger and cooling medium source. The heat exchanger itself is generally in contact with the beverage or the bowl containing the beverage. For example, one common type of dispenser incorporates a heat exchanger consisting of one or more continuous sinuous tubes submerged within the beverage in the dispenser bowl. The tubes form a heat exchanger bank that carries the cooling medium. The beverage is caused to circulate about the bank, allowing its heat to be transferred across the walls of the tubing to the flowing cooling medium. However, in such a dispenser, there must be a hole or opening through the bottom wall of the dispenser bowl to allow the tubes submerged in the beverage to be in fluid communication with the compressor and pump. Furthermore, such a construction creates a sanitation problem as the internal surfaces of the bowls and the heat exchanger bank must be cleaned with regularity, and the very shape of the heat exchanger bank poses a significant challenge to cleaning.
Therefore, alternative dispenser constructions have attempted to avoid the sanitation problem by creating a “holeless” dispenser bowl, in which the heat exchanger abuts an external surface of the bowl, commonly, the bottom wall of the bowl. Accordingly, the bottom wall of the bowl acts as an intermediary heat conductor and transfers the heat from the beverage to the flowing cooling medium of the heat exchanger.
As an alternative, co-pending and commonly assigned U.S. patent application Ser. No. 11/194,213, which is incorporated herein by this reference, describes a chilled beverage dispenser that has a “holeless” bowl and uses a cradle evaporator to achieve cooling of the beverage. Such a chilled beverage dispenser can generally be characterized as having an upper portion and a lower portion. The upper portion has a support chassis, which includes walls that collectively define a compartment for housing a dispenser bowl and a cradle evaporator. The lower portion includes a frame that defines a compartment for housing various cooling components for providing the necessary cooling medium to the cradle evaporator.
The cradle evaporator comprises three panels—a bottom panel and two side panels, the side panels being bolted or similarly fastened to the edges of the bottom panel in a substantially perpendicular orientation relative to the bottom panel, recognizing that there may be a slight draft or taper to accommodate insertion and removal of the dispenser bowl. The bottom and side panels each define a continuous and sinuous channel, which carries a cooling medium. For example, the panels may be constructed of die-cast aluminum with cast-in copper evaporator coils.
The dispenser bowl is preferably constructed of a thin-walled plastic, such that heat transfer can be achieved through the bottom and side walls of the dispenser bowl. Specifically, the bottom panel of the cradle evaporator has substantially the same size and shape and is co-extensive with the bottom wall of the dispenser bowl. Furthermore, the side panels are in contact with the side walls of the dispenser bowl over a substantial portion of the surface of each side wall.
As the cooling medium enters the cradle evaporator, it first enters the continuous and sinuous channel of the bottom panel, such that initial heat absorption is through the bottom wall of the dispenser bowl. As it completes travel through the channel of the bottom panel, the path of the cooling medium is split and directed to each of the continuous and sinuous channels of the side panels. This provides for the absorption of heat along the side walls of the dispenser bowl. Accordingly, the aforementioned sanitation problems are addressed as there is a “holeless” dispenser bowl, which can readily be lifted away from the remainder of the dispenser for cleaning. At the same time, there is no sacrifice of the effectiveness and efficiency of the cooling of the beverage because heat transfer occurs not only through the bottom wall of the dispenser bowl, but also through portions of the side walls of the dispenser bowl.
Regardless of the particular construction details and cooling techniques employed, when the dispenser includes a “holeless” bowl, there must be some consideration given as to how to appropriately agitate the beverage stored within the dispenser bowl. Specifically, in beverage dispensing equipment, a bladed impeller is commonly used to agitate, mix or pump the stored beverage. To avoid the need for a hole or opening through the bottom wall of the dispenser bowl, the bladed impeller is normally positioned within the dispenser bowl and then magnetically coupled to a rotating magnet (driven by motor) exterior to the bowl. For examples of common uses of such a magnetic impeller, reference is made to U.S. Pat. Nos. 5,931,343 and 5,209,069, each of which is assigned to the present applicant and is incorporated herein by this reference.
However, it is recognized that such impellers often draw air into the stored beverage, thus creating a vortex (i.e., turbulent flow conditions) and undesirable foaming of the beverage, especially when the stored beverage is at a low level within the dispenser bowl. Therefore, there remains a need for a pump assembly for a chilled beverage dispenser that minimizes turbulent and undesirable foaming of the beverage, while still ensuring that the beverage is effectively agitated.